1. Field of the Invention
This invention relates to a system for checking a malfunction of a controller equipped with a microcomputer.
2. Prior Art
A controller used, for example, for controlling a fuel injection in a diesel engine is equipped with a microcomputer and discrete components. Prior to the shipment of such a controller, the controller is checked to judge whether the electrical connection between the microcomputer and the discrete components is proper and to judge whether the microcomputer and the discrete components operate properly. Conventionally, these checkings are carried out, using a program for the normal control of the microcomputer. With this method, however, the inputting and outputting conditions of the controller are checked, simulating the normal control operation, so that much time and labor are required for checking a malfunction.
Controllers for air conditioners, disclosed in Japanese Laid-Open (Kokai) Patent Application Nos. 57-13517, 57-13518, 57-13519 and 57-13520, include a mode switch connected to a microcomputer. Besides the normal control mode operation, the microcomputer is programmed to judge whether the mode switch is in the ON or the OFF state and to execute a self-checking mode of operation when the mode switch is in the ON state. Prior to the shipment of the controller, the microcomputer is caused to perform the self-checking mode operation by turning on the mode switch. More specifically, light-emitting diodes connected to output ports of the microcomputer are caused to light sequentially in response to instruction signals outputted from the microcomputer. Alternatively, the light-emitting diodes are turned on or turned off in accordance with either the states of switches connected to input ports of the microcomputer or the condition of inputting of analog signals to the input ports. In this case, the operator checks whether there is any malfunction by recognizing the state (ON or OFF) of the light-emitting diodes with the eyes.
In the controllers of the above-mentioned Japanese applications, the checking of a malfunction is simplified by letting the microcomputer perform a self-checking function. However, these controllers have not been satisfactory on the following points. The self-checking function of such conventional controllers is merely to output signals in accordance with the switch signals for controlling the light-emitting diodes. Thus, a final judgment of whether there is any malfunction is left to the operator. Therefore, in the case where many inputting and outputtings of the microcomputer have to be checked, there is a risk that the operator may make a mistake in the checking.
Also, the operator must set the switches, connected to the microcomputer, to the ON or the OFF state, and therefore it is possible that the operator makes an erroneous switching operation, thus failing to carry out a proper checking.
In order to prevent a runaway (unintended operation) of the microcomputer, a detection means called "watch dog timer" is used to reset the microcomputer. Such watch dog timers are disclosed, for example, in Japanese Laid-Open (Kokai) Patent Application Nos. 58-154052, 58-155243, 58-155244, 58-155245, 60-7511, 60-8445, 61-1552, 61-8440, 61-32101 and 61-202233.